The present invention relates to open-cell/microporous molded articles with inherent latent structural convertibility, to processes for the preparation of these articles and to processes for converting their structure. The invention also relates to particular uses of the molded articles.
Within the scope of the present specification and claims, the term "molded article" is intended to include films and tubular bodies, such as tubings and hollow fibers (capillaries). By definition the term "molded article" further comprises coatings.
In the present specification and claims, microporous molded articles are to be understood as including molded articles which have effective pores of the specified size. The open-cell/microporous molded articles of this invention are hereinafter briefly called "open-cell molded articles". Molded articles according to the present invention are also referred to as intermediate products.
Open-cell/microporous plastic films are known in the art, for example, such films comprising polyamide, polysulfone or polyvinylidene fluoride (U.S. Pat. No. 3,615,024), which are produced by the so-called "phase inversion process", in which a polymer solution is cast to give a liquid film and the polymer dissolved in this liquid film is subsequently coagulated to form a dimensionally stable microporous plastic film. These prior art films are capable of absorbing liquid in their pores.
It is possible, however, only to an unsatisfactory degree to transform the known microporous films by structural conversion into a physically and/or optically, practically homogeneous and transparent state, since conversion cannot be brought about spontaneously, i.e. within a very short period, or the temperature range in which structural conversion takes place is unfavorably wide.
A film based on cellulose triacetate, which is capable of absorbing liquid, is marketed under the registered trademark POROPLASTIC. As a result of its extremely small pore size, this commercially available film is transparent. If the liquid-containing film dries out, its pore structure collapses irreversibly due to shrinkage; the film cannot be re-hydrated and it also no longer absorbs liquid.